The present invention relates generally to liquid purification apparatuses comprising an irradiation chamber for liquid purification. The present invention also relates to a beverage dispenser comprising such a purification apparatus.
One of the most essential tasks in purifying liquids such as water for drinking is disinfection, so as to ensure that any pathogenic microorganisms (e.g. bacteria, viruses, and protozoans) present in the water cannot cause illness in anyone who drinks it. It is known to perform this disinfection by the process of ultraviolet (UV) irradiation, where a volume of water being treated is bombarded with high-energy radiation in the form of UV light. The UV light damages the DNA and RNA of the pathogenic microorganisms, destroying their ability to reproduce and effectively neutralizing their ability to cause disease.
Since such systems use light to disinfect, their effectiveness is reduced on liquid which is not naturally clear or which has not been filtered to remove suspended solids. The scope of “purification,” for the purposes of this document, should thus be understood as encompassing the disinfection of liquid in which turbidity is minimal.
Traditional UV liquid purification systems have employed gas-discharge lamps as UV sources, in particular mercury-vapor lamps. Recently, it has become more and more common to employ ultraviolet light-emitting diodes (UV-LEDs) as a source of ultraviolet light for irradiation. UV-LEDs have numerous advantageous aspects which makes them appealing for use in an ultraviolet liquid purification system, notably their compact size, robustness, and lack of toxic components such as the mercury vapor found in conventional lamps. The solid-state nature of UV-LEDs also enables them to be switched on and off instantly, a further advantage relative to conventional gas-discharge lamps.
There are several examples in the prior art of UV-LEDs being employed to purify a liquid by ultraviolet irradiation. For example, the document CN 202175579 describes an irradiation device in which a single tube is spiraled around an array of UV-LEDs, and the document KR 20110007554 describes a faucet with a built-in UV-LED sterilizer for treating the liquid issuing from it. In addition, the document KR 20040073732 describes a system for purifying water that is drawn from a reservoir and conducted through a sterilizer directly to a nozzle for dispensing.
In a general manner, to ensure an efficient purification of the treated liquid, said liquid has to be irradiated by ultraviolet for a sufficient time. The known purification apparatuses commonly comprise an irradiation chamber where the liquid is irradiated. Thanks to the volume provided in this irradiation chamber, the corresponding volume of liquid may be irradiated and purified, making this volume of purified liquid immediately available. The volume of the irradiation chamber also reduces the average velocity of the liquid flowing in the irradiation chamber, thus enhancing the residence time of the liquid in said chamber, and so the irradiation time.
Typical irradiation chambers have substantially the shape of a cylinder, closed at each end by a straight wall.
The applicant has found that, in classical irradiation chamber, many dead volumes exist. “Dead volumes” are parts of the chamber where the fluid stagnates, even when a fluid stream is established in the irradiation chamber. Such dead volumes should be avoided because they reduce the effective volume of the chamber: when part of the liquid stagnates, the remaining part of the liquid in the irradiation chamber flows quicker than it would without dead volumes. Dead volumes also promote the formation of inorganic deposits in the irradiation chamber.
The applicant has also found that dead volumes generally exist around the inlet in the irradiation chamber. Thus, the liquid entering the irradiation chamber is not efficiently treated as soon as it enters the chamber, i.e. from said inlet in the irradiation chamber.
In small purification apparatuses such as those employed in water fountains, the irradiation chamber has a relatively small volume (e.g. 100 mL to 200 mL). Dead volumes are a problem particularly acute in such small irradiation chambers, because any loss in the volume actually available and used for treating the liquid should be avoided, or else, in order to obtain a certain minimum irradiation time of all the liquid flowing out of the irradiation chamber, the volume of the chamber must be increased and/or the flow rate decreased. It is not possible to wait for the fluid present in the chamber to be naturally mixed and homogenized, because generally the quantity of liquid to be delivered compared to the volume of the irradiation chamber imposes a significant continuous flow in the irradiation chamber.
Adding a mixer, which creates a turbulent flow, may be contemplated. However, using a mixer is not efficient in all reactor shapes and may have other drawbacks. For example, a power supply may be required, or this may increase the maintenance needs. Using a line having no enlarged irradiation chamber (i.e. the irradiation is performed in a portion of the hose forming the line) may be contemplated, but this is not possible in most applications because of the irradiation time required for disinfection. Placing baffles inside the irradiation chamber may also be contemplated. But the baffles create corners in the irradiation chamber which may favour the development of microorganisms and biofilm formation.
It is therefore an objective of the present invention to provide an irradiation chamber for a liquid purification apparatus using ultraviolet irradiation that solves or reduces at least one of the above mentioned drawbacks.